This invention represents an improvement over such apparatus as disclosed in U.S. Pat. No. 4,098,201 issued July 4, 1978 to M. Adamski, Jr. et al. However, this invention is equally applicable, at least in part, to other types of machines which are adapted to operate on the edge of a workpiece.
The present invention relates to sewing machines and more particularly to an auxiliary feed mechanism which is capable of being attached to existing machines for feeding a workpiece past a work station of the machine where operations are performed thereon.
It is recognized that it may be desirous in some operations to aid the feed mechanism of the machine in continually advancing the workpiece through the work station and, in some instances, to continue running after the machine stops in order to pull the material through the machine. It may also be a common desire in some sewing operations to intermittently alter the speed of the machine so as to gather or stretch the fabric plies and then return the sewing machine to its normal or regular operating speed. While the present invention may be capable of performing these operations and others, for purposes of this description the present invention will be described for and in terms of an apparatus as applied to a stitching machine of the type described in the above identified patents wherein a blindstitch hem is secured about the edge of a tubular garment such as a T-shirt.
As one skilled in the art may appreciate, in hemming tubular workpieces it is necessary to carefully control the position of the workpiece edge relative the workstation of the machine. With the machine described in the above identified patent, that portion of the workpiece to be hemmed is rotated in a true circle. However, at the onset of the sewing cycle a portion of the workpiece immediately rearward of the presser foot may be laterally displaced relative the portion of the edge in advance of the stitch forming area. In view of the circular rotation of the raw edge and so as to aid in advancing and guiding the workpiece through the machine, means are provided for realigning and maintaining the workpiece edge within certain limits.
The industrial sewing machine industry has consistently sought ways by which an auxiliary feed action may be placed upon the workpiece as the latter is fed through the stitching area of the machine. It has been known in industrial type sewing machines to impart a concomitant feeding motion to the workpiece by use of a puller mechanism assembly which assists the sewing head during the sewing operation. Attempts have been made by using pullers which include upper and lower (top and bottom) rollers which contact the fabric after sewing so as to pull the workpiece through the sewing station. As is apparent, if any puller mechanism is going to aid in advancing the workpiece it is required to move slightly in excess of the speed of the feed mechanism of the machine. However, the excess speed requirement sometimes requires the use of additional mechanisms so as to achieve the desired ratio as well as to allow adjustment of said ratio.
Such devices known for concomitantly feeding the workpiece in relation with the feed mechanism of the machine have the disadvantage of usually requiring cumbersome supports and guides which are normally situated about the sewing head so as to derive power therefrom. This leads to another disadvantage, in that the higher speeds of today's machines require a minimum of loading to be placed on the machine so that quick acceleration and higher speeds may be achieved. As mentioned above, and as should be apparent, auxiliary feed mechanisms are usually set to run faster than the speed at which the feed mechanism is advancing the material workpiece but unless this quicker speed is calculated quite carefully, undesired gathering of the material workpiece may result. In this regard, the lack of an adequate adjustability factor is yet another drawback in the heretofore known devices. That is, once the speed of the auxiliary feed mechanism has been adjusted it has not been possible to readily vary the speeds of said mechanism during sewing. Further with the heretofore known devices the speed of the auxiliary feed mechanism is usually not fully developed until the sewing machine has attained its full or required speed. But, whereas it is desirous to achieve the full speed of the auxiliary feed mechanism concurrent with the speed of the machine so as to advance the workpiece in conjunction with the speed of the feed mechanism. It has also been known to provide means in front of the stitching devices for forcibly urging the workpiece edge into alignment with a predetermined position. As one will appreciate, the forceful urging of workpiece edge in close proximity to the stitching device without some regard to the speed of the feed mechanism may cause puckering or uneven seams. For the reasons discussed hereinabove, the art heretofore known does not readily lend itself to the application required with the machine shown in the above identified patent.
In addition, it may be interesting to note that the same or seemingly similar types of material may sew quite differently depending on variations in the finish of the workpiece, it's color and possibly even if it has been compacted in storage. Although these variations may not matter a great deal in a conventional sewing operation, they may affect the operation of the bottom hemmer due to its automatic rather than manual operation. Therefore, it was necessary to provide means which could quickly and easily compensate for any variances in the workpieces being sewn.